Coaxial resonant line coupling means



p 1953 I T. E. MOORE ETAL COAXIAL. RESONANT LINE COUPLING MEANS Filed April 30, 1946 FIG.[

HOWARD M. ZEIDLER QLZM,

ATTORNEY Patented Sept. 22 195? COAX'IAL RESONANT LINE COUPLING MEANS Thomas E. Moore, Austin, Tex., and Karl R. Spangenberg'and Howard M. Zeidler, Palo Alto, Calif., assignors to the United States of America as represented by the Secretary of War Application April 30, 1946, Serial No. 666,002

3 Claims. 1 This invention relates generally to a radio frequency coupling means and more particularly to a composite probe-loop coupler.

One method for extracting radio frequency energy from a resonant cavity employs either a loop coupler or a probe coupler, depending uponv the wavelength and upon the type of field which exists in the cavity at the coupler position. A loop coupler projects into the cavity at a lowimpedance region of the cavity whereas a probe coupler is introduced into a high-impedance region of the cavity. In some oscillators, it is impossible to position either a simple loop or a simple probe in such a region of the cavity that adequate power will be coupled from the oscillator over the entire tuning range. An object of the present invention is to provide a composite probeloop coupler which is energized by a magnetic field throughout part of a frequency range, and electrostatically throughout the remainder. In this respect, the composite coupler will function as a so-called broad band coupler in that it will be operable between fairly wide frequency limits.

In one type of microwave oscillator, a resonant coaxial line section is employed as the frequency determining element in combination with a vacuum tube. An adjustable plunger within the coaxial line is positioned such that the length of the coaxial line is substantially or% of a Wavelength at the operation frequency. For extremely high frequencies, the plunger must necessarily be positioned very close to the vacuum tube itself, and the physical dimensions of the line structure will then be extremely small. The only fixed position at which a non-composite type of coupler could be placed, and at the same time afford optimum coupling over a broad tuning range, would be at a high impedance point within the vacuum tube itself. This is not always possible. Therefore, another object of the present invention is to adapt the composite probe-loop coupler embodying the principles of this invention for use in a fixed position within a resonant coaxial line.

A loop or probe coupling means which is used for extracting radio frequency energy from an enclosure may also be used for injecting radio frequency energy into and thereby exciting an electric field within the enclosure. It is a further object of the invention that the composite coupler embodying the principles of this invention be adapted for the injection of radio frequency energy into an enclosure as well as the extraction therefrom. And still another object is that the composite coupler embodying the principles of this invention shall be simple, compact, and possess broad band characteristics.

Other objects, features and advantages of this invention will suggest themselves to those skilled in the art, and will become apparent from the following description of the invention, taken in connection with the accompanying drawings, in which:

Fig. 1 is a cross-sectional view of a composite probe-loop coupler embodying the principles of this invention; and

Fig. 2 is a cross-sectional view of a selected resonant coaxial line including the composite coupler shown in Fig. 1.

The composite coupler of this invention may consist essentially of a loop-probe ii) embedded, over most of its length, inside a cylindrically shaped dielectric slug II which is surrounded by a hollow metallic tube l2. Tube l2 projects through a hole 13 in outer wall M of a cavity structure ll, and is in electrical contact with wall It. Surface 14' is the inside surface of the cavity structure.

Loop-probe It! comprises a solid conductor l5 bent in substantially a rectangular shape and embedded in the dielectric slug. One portion of the loop-probe It! projects out through the bottom of the dielectric slug ll into the free space of cavity IT to form a loop I8. One end of conductor l5 emerges from the dielectric slug II and is electrically connected to point It on tube The opposite end of conductor l5 projects out of the top of dielectric slug H, and is connected to the center conductor 20 of coaxial output cable 21. Outer conductor 22 of coaxial output cable 2i is electrically connected to hollow tube I2. Cable 2| may include a dielectric material it between center conductor 20 and outer conductor 22.

The length L in Fig. 1 refers to the length of the loop-probe ID from point It to the tip of loop I 8. For a fixed length L, the composite loop-probe to functions substantially as a loop or as a probe, depending upon the wavelength A, as measured in the dielectric material, of the radio frequency energy applied to the coupler. For any radio frequency energy having a wavelength satisfying Equation 1 shown below, the loop-probe short at point It reflects to the tip of loop It as a low impedance.

where n is any integer 1, 2, 3,

The tip of loop I8 is effectively shorted to the inside Wall M of cavity H, and the composite loop-probe functions substantially as a loop projecting within the cavity. The loop coupling is characterized byhaving a high coupling factor C as defined by Equation 2 shown below.

C=A1/Aw (2) where:

A1=eflective area of the loop intercepted by the cavity; and

Aw=effective area of the wire surface protruding into the cavity.

For any radio frequency saving a wavelength l, and satisfying Equation 3 shown below, the loop-probe short at point [6 is referred to the tip of loop It as a high impedance.

where i=0, 1, 2,- 3', 4, 5',

Forthis conditiomthe loop -probe corresponds to a straight probe which projectsinto thecavity.

The probe coupling is characterized by having a lo coupling factor C as defined by Equation 2 Shawn state. The coupling factor inay be eifectively reduced for the case of the probe coupler by the addition o'f a small plate (not Shown) to the tip Of loop 58; I It will be evident to those skilled in the art that at frequencies having wavelengths intermediate to those specifically defined, composite loop-probe it may function substantially as a combination loop and probe;

selected coaxial resonant line utilizing the composite coupler embodying the principles of this invention; and such as might be employed a; microwave oscillator, is shown in Fig. 2. High frequency energy supplied to the line section through aperture 59 by well known means; As mentioned heretofore, the invention contemplates a composite coupling means which is u es 11s extract radio frequency energy over substantially broad frequency limits from the co xial resonant line. The resonant line compr es an annularly shaped inclosure lie formed a ceirter conductor 51, end plate portions 52 and 53, and theconcentrically spaced outer conductor 5 Annular plunger 55 is set within "ur'e Siiiiia v plane transverse to the axis of center conductor 5i. Its inner and outer euges arein electrical contact with the inner surface of outer conductor 5 and the outer s rracebr center conductor 5| by means of friccontacts 48-. Plunger 55 is adjusted from o a role the section by suitable means, such as rods 56. attached thereto and projecting through holes 5'] in portion 53 I.

Plunger 55 is positioned such that a section 53 in inclosure 50 being formed by end portion 5 2; plunger 55, and a section of the outer conductorbecomes resonant at the particular rad-i0 freciue'ncy energyinjected therein. Oscillations are thereby sustained within resonant section 58. Composite loop-probe it projects through hole IS in portion 52. The structural features of the composite loop-probe embodying the principles of this invention have already been described in connection with Fig. l. The length L in Fig. 2 corresponds to the length L in reference to Fig. 1. Radio frequency energy extracted from the cavity by the loop-probe it is conducted out by means of output coaxial line 2|.

When such a resonant line is incorporated in a microwave radio frequency oscillator which utilizes a wavelength resonant line, plunger 55 is positioned substantially wavelength at the operated frequency from end portion 52. A strong electric field having a wavelength A will exist in the resonant section 58, and composite loop-probe ID will extract radio frequency energy from the section over limits defined by the maximum wavelength Milan and the minimum wavelength )unin, where Mnax is approximately equal to two' times mm. For such frequency limits, the length L of loop-probe i0 is substantially ra /4 or stated alternatively is equal to 7\max/8- When such a resonant line is incorporated in a microwave oscillator which utilizes a onequarter wavelength resonant line, plunger 55 is positioned substantially one-quarter wavelength at the operating frequency from end portion 52; For such-a resonant line and for the operating frequency limits of Ammto )u'nax; mentioned heretofore, the length L of loop-probe [0 is substantially Main/2 or stated alternatively max/ i.- For any other applications having similar frequency range limitations, the length L is adjusted accordingly. g I

Such compo-site p-robeeloo coupler is adapted for coupling together a plurality of resonant line such 7 might be used between the anode-g the grid cathoderesonant line sections of a radio frequency oscillator. It may also be inccr orated as the coupling means between a plura of resonant cavities.

The composite probe-loop coupler has been described in connection wi-th the extraction of radio uency energy from a cavity or resonant line. also adapted for injecting radio frequency energy intoa coaizialline or cavity and excitin an electric field therein;

Ehe composite probe-loop coupler is simple compact, and allows satisfactory wide band ccuplig even in those cases where the probeloop cannot be located at the op. cum point in the cavity or resonant line. In the Ill/e oscillator, effective probe coupling is acni red at the short wavelength limit, and lcop proce coupling at the long wavelength limit.- In the l/e oscillater. effective loop c upling is achieved at the short wavelength li'. and effective probe coupling at the long wavelength limit. 7

While there been described here .above what is at present considered to be; a preferred embodiment of ti invention, it w'l be obvious to those skilled the art that various changes and modifications may be made therein without departing from he true and scope of the invention.

What is claimed is: h

l. A composite prebedoop coupler comprising a ieetric. slug; a hollow tube enclosing said dielec trio and an elongated ductor passing through said tube and having c e end protruding out of one end of slug, the other end of said conductor being doubled bacli to f a leop=,,said 1001} having a flllSt portion embedded in dielectric slug and a second p lon protruding out of the other end of sa d and out of one end of said tube; said end of said condr tor being connected said tube at a substantial distance from said one end of said tube, said having an elongated, substantially rectaneu r shape with its longer dimension being effectrvely equal ta a quarter wave length at an operating frequency of said coupler.

2. A composite probe-loop coupler for operation between the limits of two given frequencies, the first of said frequencies being twice that of the second of said frequencies, comprising a hollow conductive tube, and a conductor passing through said tube and having one end doubled back within said tube to form a loop, said loop being partially inside said tube with an outer portion extending outside of one end of said tube, said one end of said conductor being shorted to said tube at a distance from the tip of said outer portion of said loop that is effectively equal to an odd number of quarter wavelengths at said second frequency and an integral number of half wave lengths at said first frequency.

3. The coupler of claim 2 further including a dielectric slug disposed within said hollow tube References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 10 2,311,520 Clifford Feb. 16, 1943 2,351,895 Allerding June 20, 1944 2,401,637 Harries June 4, 1946 2,404,542 Sloan July 23, 1946 2,423,416 Sontheimer July 1, 1947 15 2,490,845 Sorg Dec. 13, 1949 2,550,524 Braden Apr. 24, 1951 and substantially about the portion of said loop within said tube.

THOMAS E. MOORE. KARL R. SPANGENBERG. HOWARD M. ZEIDLER. 

